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<h1>Penlight</h1>

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<h1>Module <code>pl.class</code></h1>
<p>Provides a reuseable and convenient framework for creating classes in Lua.</p>
<p> Two possible notations:</p>


<pre>
B = class(A)
class.B(A)
</pre>

<p> The latter form creates a named class within the current environment. Note
 that this implicitly brings in <a href="../libraries/pl.utils.html#">pl.utils</a> as a dependency.</p>

<p> See the Guide for further <a href="../manual/01-introduction.md.html#Simplifying_Object_Oriented_Programming_in_Lua">discussion</a></p>


<h2><a href="#Functions">Functions</a></h2>
<table class="function_list">
	<tr>
	<td class="name" nowrap><a href="#_init">_init (...)</a></td>
	<td class="summary">initializes an <strong>instance</strong> upon creation.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#instance:is_a">instance:is_a (some_class)</a></td>
	<td class="summary">checks whether an <strong>instance</strong> is derived from some class.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#some_class:class_of">some_class:class_of (some_instance)</a></td>
	<td class="summary">checks whether an <strong>instance</strong> is derived from some class.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#some_class:cast">some_class:cast (some_instance)</a></td>
	<td class="summary">cast an object to another class.</td>
	</tr>
	<tr>
	<td class="name" nowrap><a href="#class">class (base, c_arg, c)</a></td>
	<td class="summary">create a new class, derived from a given base class.</td>
	</tr>
</table>

<br/>
<br/>


    <h2 class="section-header "><a name="Functions"></a>Functions</h2>

    <dl class="function">
    <dt>
    <a name = "_init"></a>
    <strong>_init (...)</strong>
    </dt>
    <dd>
    initializes an <strong>instance</strong> upon creation.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">...</span>
         parameters passed to the constructor
        </li>
    </ul>




    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> Cat = class()
<span class="keyword">function</span> Cat:_init(name)
  <span class="comment">--self:super(name)   -- call the ancestor initializer if needed
</span>  self.name = name
<span class="keyword">end</span>

<span class="keyword">local</span> pussycat = Cat(<span class="string">"pussycat"</span>)
<span class="global">print</span>(pussycat.name)  <span class="comment">--&gt; pussycat</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "instance:is_a"></a>
    <strong>instance:is_a (some_class)</strong>
    </dt>
    <dd>
    checks whether an <strong>instance</strong> is derived from some class.
 Works the other way around as <a href="../libraries/pl.class.html#some_class:class_of">class_of</a>. It has two ways of using;
 1) call with a class to check against, 2) call without params.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">some_class</span>
         class to check against, or <code>nil</code> to return the class
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        <code>true</code> if <code>instance</code> is derived from <code>some_class</code>, or if <code>some_class == nil</code> then
 it returns the class table of the instance
    </ol>



    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> pussycat = Lion()  <span class="comment">-- assuming Lion derives from Cat
</span><span class="keyword">if</span> pussycat:is_a(Cat) <span class="keyword">then</span>
  <span class="comment">-- it's true, it is a Lion, but also a Cat
</span><span class="keyword">end</span>

<span class="keyword">if</span> pussycat:is_a() == Lion <span class="keyword">then</span>
  <span class="comment">-- It's true
</span><span class="keyword">end</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "some_class:class_of"></a>
    <strong>some_class:class_of (some_instance)</strong>
    </dt>
    <dd>
    checks whether an <strong>instance</strong> is derived from some class.
 Works the other way around as <a href="../libraries/pl.class.html#instance:is_a">is_a</a>.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">some_instance</span>
         instance to check against
        </li>
    </ul>

    <h3>Returns:</h3>
    <ol>

        <code>true</code> if <code>some_instance</code> is derived from <code>some_class</code>
    </ol>



    <h3>Usage:</h3>
    <ul>
        <pre class="example"><span class="keyword">local</span> pussycat = Lion()  <span class="comment">-- assuming Lion derives from Cat
</span><span class="keyword">if</span> Cat:class_of(pussycat) <span class="keyword">then</span>
  <span class="comment">-- it's true
</span><span class="keyword">end</span></pre>
    </ul>

</dd>
    <dt>
    <a name = "some_class:cast"></a>
    <strong>some_class:cast (some_instance)</strong>
    </dt>
    <dd>
    cast an object to another class.
 It is not clever (or safe!) so use carefully.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">some_instance</span>
         the object to be changed
        </li>
    </ul>





</dd>
    <dt>
    <a name = "class"></a>
    <strong>class (base, c_arg, c)</strong>
    </dt>
    <dd>
    create a new class, derived from a given base class.
 Supporting two class creation syntaxes:
 either <code>Name = class(base)</code> or <code>class.Name(base)</code>.
 The first form returns the class directly and does not set its <code>_name</code>.
 The second form creates a variable <code>Name</code> in the current environment set
 to the class, and also sets <code>_name</code>.


    <h3>Parameters:</h3>
    <ul>
        <li><span class="parameter">base</span>
         optional base class
        </li>
        <li><span class="parameter">c_arg</span>
         optional parameter to class constructor
        </li>
        <li><span class="parameter">c</span>
         optional table to be used as class
        </li>
    </ul>





</dd>
</dl>


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